Feasibility study on the use of Coprostanol to identify the source of nitrate groundwater pollution

Investigation of contaminant sources is indispensable to develop effective countermeasures against nitrate (NO3-) pollution in groundwater. Major nitrogen (N) sources are chemical fertilizer, livestock waste, and domestic wastewater. The scatter diagram of δ18O and δ15N of NO3- (Kendall, 1998) has been used to identify pollution sources. However, it can be difficult to distinguish sources because of the overlapping δ18O and δ15N ranges of chemical fertilizer and livestock waste sources. In this study, we propose the use of Coprostanol as a method to identify source of the pollution. Coprostanol has been used as a fecal contamination indicator because it is one of the major fecal sterols formed by the conversion of cholesterol by intestinal bacteria in the gut of higher animals. The proposed method was applied to the case of NO3-pollution in Shimabara, Nagasaki, Japan. Water samples were collected at 33 locations from March 2011 to November 2014, then the relationships among NO3-N, δ15N-NO3-, δ18O-NO3- and Coprostanol were evaluated. We found no relationship between polluted NO3- (> 10 mg L-1) and Coprostanol concentrations. This polluted group includes samples containing lower levels of Coprostanol (< 200 ng L-1). Fertilizer is likely to be the predominant source of NO3-in these lower level samples. According to the scatter diagram proposed by Kendall (1998), the plotted results were concentrated in the overlapping region of fertilizer and livestock waste sources. Therefore, it remains difficult to distinguish pollution sources. To perform more clear assessment, we plotted the relationship between Coprostanol concentration and δ15N. However, no clear relation was observed. Higher level Coprostanol (> 300 ng L-1) samples corresponded to the polluted sample group obtained from cluster analysis (Nakagawa et al., 2016). Therefore, Coprostanol has some potential for source identification of NO3-pollution.